Method of producing dense sintered silicon carbide body from polycarbosilanes

Abstract

A method of producing a sintered silicon carbide body high in density, flexural strength and purity at elevated temperatures from polycarbosilanes is disclosed. The method involves the following steps: (A) polymerizing organosilicon compounds to yield specific polycarbosilanes which are insoluble in solvents and unmeltable i.e. the polycarbosilanes being higher in melting temperature or in softening temperature than in thermal decomposition temperature; (B) pulverizing the insoluble and unmeltable polycarbosilanes so as to form a powder; (C) applying heat with or without the use of pressure to the powder charged into a hot press mold in a nonoxidizing atmosphere to thereby decompose the same thermally into silicon carbide and sintering the silicon carbide under pressure.

What we claim is: 
     
       1. A method of producing a dense sintered silicon carbide body from polycarbosilane comprising the steps of: (A) Polymerizing an organosilicon compound to yield polycarbosilane, said polycarbosilane being insoluble and unmeltable;   (B) Pulverizing said polycarbosilane so as to form a powder; and   (C) Hot pressing said powder so as to produce said dense sintered silicon carbide body by charging said powder into a hot press mold, heating said powder in a nonoxidizing atmosphere to thereby decompose said powder thus producing silicon carbide, and sintering said silicon carbide under pressure.   
     
     
       2. A method according to claim 1, wherein said thermal decomposition in the Step (C) is carried out in a temperature range of 600° to 1000° C. 
     
     
       3. A method according to claim 1, wherein said sintering in the Step (C) is carried out in a temperature range of 1900° to 2200° C under a pressure of up to 250 kg/cm 2 . 
     
     
       4. A method according to claim 1, wherein the hot pressing Step (C) further includes exhausting from said mold the gas produced as a by-product by said thermal decomposition. 
     
     
       5. A method of producing a dense sintered silicon carbide body from polycarbosilane comprising the steps of: (A) polymerizing organosilicon compounds so as to form an insoluble, unmeltable polycarbosilane,   (B) pulverizing said polycarbosilane to provide a powder and mixing said powder with a sintering aid to provide a mixture, and   (C) hot pressing said mixture in a hot press mold so as to produce said dense sintered silicon carbide body by heating said mixture in a nonoxidizing atmosphere to thereby decompose said polycarbosilane so as to form silicon carbide, and sintering said silicon carbide under pressure.   
     
     
       6. A method according to claim 5, wherein said sintering aid is selected from the group consisting of the elements of B, C, Al, Fe, Ga, Ti, W, Mg, Ca, Ni, Cr, Mn, Zn, In, Sc, and Be, and compounds of said elements. 
     
     
       7. A method according to claim 5, wherein said sintering aid is selected from a group consisting of B 4  C, Fe, Al, ZrB 2 , W and MgO. 
     
     
       8. A method according to claim 5, wherein the amount of said sintering aid is in the range of 0.3 to 1.0% by weight based on said polycarbosilane powder. 
     
     
       9. A method according to claim 5, wherein said thermal decomposition in the Step (C) is carried out in a temperature range of 600° to 1000° C. 
     
     
       10. A method according to claim 5, wherein said sintering in the Step (C) is carried out in a temperature range of 1900° to 2200° C under a pressure of up to 250 kg/cm 2 . 
     
     
       11. A method according to claim 5, wherein the hot pressing step (C) further includes exhausting from said mold the gas produced as a by-product by said thermal decomposition. 
     
     
       12. A method of producing a dense sintered silicon carbide body from polycarbosilane comprising the steps of: (A) polymerizing an organosilican compound with addition of a sintering aid so as to form an insoluble and unmeltable polycarbosilane containing said sintering aid,   (B) pulverizing said polycarbosilane to provide a powder,   (C) hot pressing said powder so as to produce said dense sintered silicon carbide body by charging said powder into a hot press mold, heating the powder in a nonoxidizing atmosphere to thereby decompose said powder so as to produce silicon carbide, and sintering said silicon carbide under pressure.   
     
     
       13. A method according to claim 12, wherein said sintering aid is selected from a group consisting of the elements of B, C, Al, Fe, Ga, Ti, W, Mg, Ca, Ni, Cr, Mn, Zr, In, Sc and Be, and compounds of said elements. 
     
     
       14. A method according to claim 12, wherein said sintering aid is from a group consisting of the elements of B, Al, Fe and Ti, halides and organic compounds of said elements. 
     
     
       15. A method according to claim 12, wherein said sintering aid is added so as to yield said polycarbosilane containing therein 0.1 to 3.0% by weight of the element of B, Al, Fe and Ti. 
     
     
       16. A method according to claim 12, wherein said thermal decomposition in the Step (C) is carried out in a temperature range of 600° to 1000° C. 
     
     
       17. A method according to claim 12, wherein said sintering in the Step (C) is carried out in a temperature range of 1830 to 2100° C under a pressure of up to 250 kg/cm 2 . 
     
     
       18. A method according to claim 12, wherein the hot pressing Step (C) further includes exhausintg from said mold the gas produced as a by-product of said thermal decomposition. 
     
     
       19. A method according to claim 1 wherein said powder produced in step (B) has a size of less than about 100 mesh. 
     
     
       20. A method according to claim 5 wherein said powder produced in step (B) has a size of less than about 100 mesh. 
     
     
       21. A method according to claim 12 wherein said powder produced in step (B) has a size of less than about 100 mesh.